CN117134406A - Virtual synchronous machine-based control method and system for network-structured flexible direct current system - Google Patents
Virtual synchronous machine-based control method and system for network-structured flexible direct current system Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/381—Dispersed generators
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/24—Arrangements for preventing or reducing oscillations of power in networks
- H02J3/241—The oscillation concerning frequency
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/388—Islanding, i.e. disconnection of local power supply from the network
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
- H02J2003/365—Reducing harmonics or oscillations in HVDC
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- H—ELECTRICITY
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
The application discloses a control method and a control system of a net-structured flexible direct current system based on a virtual synchronous machine, which are based on a virtual synchronous control second-order model, reference a third-order generator model, and consider transient processes of a speed regulator and an excitation winding, so that the flexible direct current system has the capability of improving system voltage and frequency stability and enhancing system inertia and damping. The control method can flexibly perform island/networking operation mode conversion, and can effectively solve the problem that a flexible direct control strategy is not suitable due to the change of the power grid strength.
Description
Technical Field
The application relates to the technical field of flexible direct current transmission, in particular to a method and a system for controlling a network-structured flexible direct current system based on a virtual synchronous machine.
Background
With more and more high voltage class, high capacity flexible dc engineering, operation is continued. Compared with the traditional high-voltage direct current engineering, the flexible direct current engineering has the advantages of high response speed, flexible decoupling control of active power and reactive power, low harmonic level, no commutation failure problem, low transmission loss, easiness in realizing tide inversion, capability of independently supplying power to a passive system and the like, and is widely applied.
The core device of the flexible direct current system is a modularized multi-level converter, and the response characteristic of the core device is far superior to that of a synchronous generator which is the core device of a traditional power system. With the continuous access of a flexible direct current system and renewable energy sources, the power system presents a high-proportion power electronic trend, and the problems of system inertia reduction, frequency stability reduction, multi-frequency band oscillation and the like are endless. For example, yubei, zhang Bei, such as east, bus and other engineering topological structures are complex, various operation modes such as networking, island operation and the like exist at a transmitting and receiving end, great difference exists between the intensity degree of an alternating current system, the problems of broadband oscillation and transient overvoltage are outstanding, and huge operation pressure and risk exist in the system.
In order to solve the above problems, many scholars propose to adopt a grid-type inverter control technology to enable the soft and straight primary frequency modulation capability and inertia characteristics. The network control corresponds to the network control adopted by the traditional converter, and the control can realize synchronization without a phase-locked loop. Typical web-formed flexible-straight control techniques include droop control, VF control, and the like. Droop control simulates droop characteristics of synchronous generators P-f and Q-U, has high response speed, but does not have inertia and damping characteristics, and is easy to cause voltage and frequency oscillation. VF control simulates an infinitely large power supply, is a passive control, but cannot simulate the active-frequency and virtual inertia, reactive-voltage and virtual excitation regulation characteristics of a synchronous generator, and the application range is limited. Therefore, it is valuable to research a net-structured flexible-direct control strategy capable of simulating the external support characteristic of the synchronous generator.
Most of the existing flexible direct current systems use a grid-following control working mode with current source characteristics, and the phase information of grid-connecting points is measured by a phase-locked loop to realize synchronization with a power grid. In the dq coordinate system, the heel-net control can be decomposed into an inner loop current controller and an outer loop power controller. Typical pll control is shown in fig. 2, and pll-based dual loop control of a grid-connected flexible dc converter is shown in fig. 3.
In the prior art, the dual-loop control of the follow-grid type flexible direct current system based on the phase-locked loop can only be operated in a grid-connected mode, cannot be independently operated, has lower grid-connected stability under the conditions of weak system strength and low inertia, and cannot actively support the voltage of a power grid and the inertia of the system.
Disclosure of Invention
In order to solve the technical problems, the application provides a control method of a network-structured flexible direct current system based on a virtual synchronous machine, which comprises the following steps:
establishing a third-order virtual synchronous machine control model applied to the flexible direct current converter according to a second-order rotor model and a third-order generator model of the virtual synchronous machine;
applying the third-order virtual synchronous machine control model, and responding to the system frequency change by introducing a virtual speed regulator in the primary frequency modulation process of the virtual synchronous machine; obtaining a synchronous generator rotor motion equation through sagging control;
the method comprises the steps of simulating a rotor motion equation of the synchronous generator, regarding an active power reference value of an inverter as mechanical power of the synchronous generator, and adjusting the rotating speed of the synchronous generator according to the change of the mechanical power so as to change a phase angle;
based on the third-order virtual synchronous machine control model, simulating an excitation voltage regulating system of the synchronous generator, taking the deviation of a net side alternating voltage measured value and a reference value as the input of the excitation voltage regulating system of the synchronous generator, and regulating reactive exchange of the soft direct current converter and the excitation voltage regulating system of the synchronous generator by changing the virtual internal potential amplitude;
calculating a corresponding current reference value according to the phase angle, the virtual internal potential amplitude and the primary characteristic of the converter;
taking the deviation of the current reference value and the real side value as input, and obtaining a voltage reference value of the soft direct current converter after superposition decoupling voltage and cross compensation; obtaining a voltage reference wave under the three-phase static coordinate-sensitive magic according to the phase angle of the virtual internal potential; and generating trigger pulses according to the voltage reference waves, and respectively controlling all sub-bridge arm sub-modules of the flexible direct current converter.
Further, according to the second-order rotor model and the third-order generator model of the virtual synchronous machine, a third-order virtual synchronous machine control model applied to the flexible direct current converter is established, and the method comprises the following steps:
according to a second-order rotor model and a third-order generator model of the virtual synchronous machine, the influences of a virtual speed regulator, a rotor motion equation, a damping factor D, a rotor voltage balance equation and an excitation winding transient process are calculated, stator D and q winding transient processes are ignored, an improved virtual synchronous control model is simplified and obtained, specifically,
wherein θ is the internal potential virtual phase angle; omega is the virtual angular velocity of the controller; j is virtual inertia; p (P) m Is virtual mechanical power; p (P) e The active power is actually output for the flexible and straight system; d is a damping coefficient; omega 0 Is the angular velocity of the system; t (T) d ' 0 Is the excitation winding time constant; e's' q Is a transient potential; e (E) qe Is a forced no-load electromotive force; i.e d The d-axis current component is taken as the d-axis current reference value I of the converter output dref ；x d Is a synchronous reactance; x's' d Is the d-axis transient reactance.
Further, obtaining a synchronous generator rotor motion equation through droop control includes:
when the deviation between the measured value and the reference value of the system frequency exceeds the dead zone link, multiplying the dead zone link by a droop coefficient to generate additional power, performing a rotor motion equation through droop control,
wherein DeltaP ref Is an additional reference power; k (K) p Is a sagging coefficient; f (f) * Is the reference frequency; f is the measured frequency; f (f) deadzone To set the frequency dead zone.
Further, adjusting the rotational speed of the synchronous generator according to the mechanical power change, thereby changing the phase angle, includes:
the rotor inertia integration link and damping component are introduced in the generation process of the phase angle, so that the power and the frequency approximate synchronize the generator in the dynamic process,
wherein DeltaP ref And (5) providing additional reference power for the virtual speed regulation control link.
Further, taking the deviation of the net side alternating voltage measured value and the reference value as the input of the synchronous generator excitation voltage regulating system, and regulating the reactive exchange of the soft direct current converter and the synchronous generator excitation voltage regulating system by changing the virtual internal potential amplitude, comprising:
the deviation of the net side alternating voltage measured value and the reference value is used as the input of the excitation voltage regulating system of the synchronous generator, the virtual internal potential amplitude is changed through PID amplitude limiting control, a lead-lag link, a rotor voltage balance equation and a first-order inertia link, and then the reactive power exchange between the soft direct current converter and the system is regulated,
wherein E is qe Is a forced no-load electromotive force in linear relation with the exciting voltage; k is the regulator gain; k (K) v Selecting a factor for proportional integral; t (T) 1 、T 2 、T 3 、T 4 Is the voltage regulator time constant; u (U) sref Is an inverter ac voltage reference value; u (U) s Is the actual measurement value of the alternating voltage; e (E) m The internal potential amplitude is output for the inverter.
Further, according to the phase angle, the virtual internal potential amplitude and the primary characteristic of the converter, a corresponding current reference value is calculated, including:
assuming a prescribed internal potential dq axis reference value U cdref And U cqref The d-axis direction of (2) coincides with the virtual internal potential direction, and there are:
the current reference value is:
wherein I is dref +jI qref Is an output current reference value; u (U) cdref +jU cqref Is a virtual internal potential; u (U) sd +jU sq Is the actual ac side voltage; r+jx is the branch impedance.
Further, the method further comprises the following steps:
determining the limiting value I of the current according to the low-voltage current-limiting curve of the system-side alternating voltage dqlim And the current reference value after the limiting link enters the inner ring control again.
The application also provides a control system of the network-structured flexible direct current system based on the virtual synchronous machine, which comprises:
the third-order model construction module is used for building a third-order virtual synchronous machine control model applied to the flexible direct current converter according to the second-order rotor model and the third-order generator model of the virtual synchronous machine;
the motion equation obtaining module is used for applying the third-order virtual synchronous machine control model, and responding to the system frequency change by introducing a virtual speed regulator in the primary frequency modulation process of the virtual synchronous machine; obtaining a synchronous generator rotor motion equation through sagging control;
the phase angle obtaining module is used for regarding the active power reference value of the converter as the mechanical power of the synchronous generator by simulating the motion equation of the rotor of the synchronous generator, and adjusting the rotating speed of the synchronous generator according to the change of the mechanical power so as to change the phase angle;
the reactive power exchange module is used for simulating an excitation voltage regulating system of the synchronous generator based on the third-order virtual synchronous machine control model, taking the deviation of the net side alternating voltage measured value and the reference value as the input of the excitation voltage regulating system of the synchronous generator, and adjusting the reactive power exchange of the soft direct current converter and the excitation voltage regulating system of the synchronous generator by changing the virtual internal potential amplitude;
the current reference value calculation module is used for calculating a corresponding current reference value according to the phase angle, the virtual internal potential amplitude and the primary characteristic of the converter;
the control module is used for taking the deviation of the current reference value and the real side value as input, and obtaining the voltage reference value of the soft direct current converter after superposition decoupling voltage and cross compensation; obtaining a voltage reference wave under the three-phase static coordinate-sensitive magic according to the phase angle of the virtual internal potential; and generating trigger pulses according to the voltage reference waves, and respectively controlling all sub-bridge arm sub-modules of the flexible direct current converter.
Further, the current reference value calculation module includes:
a calculation sub-module for assuming a prescribed internal potential dq axis reference value U cdref And U cqref The d-axis direction of (2) coincides with the virtual internal potential direction, and there are:
the current reference value is:
wherein I is dref +jI qref To output electricityA stream reference value; u (U) cdref +jU cqref Is a virtual internal potential; u (U) sd +jU sq Is the actual ac side voltage; r+jx is the branch impedance.
Further, the method further comprises the following steps:
a limiting submodule for determining the limiting value I of the current according to the low-voltage current-limiting curve of the system side alternating voltage dqlim And the current reference value after the limiting link enters the inner ring control again.
According to the control method and system for the net-structured flexible direct current system based on the virtual synchronous machine, the third-order generator model is referenced on the basis of the virtual synchronous control second-order model, and the transient processes of the speed regulator and the exciting winding are considered, so that the flexible direct current system has the capabilities of improving the voltage and frequency stability of the system and enhancing the inertia and damping of the system. The control method can flexibly perform island/networking operation mode conversion, can effectively solve the problem that a flexible direct-current control strategy is not suitable for caused by the change of the power grid strength, and is an important foundation for popularization and application of the network construction type flexible direct-current transmission technology.
Drawings
Fig. 1 is a schematic flow chart of a control method of a network-structured flexible direct current system based on a virtual synchronous machine;
fig. 2 is a phase-locked loop control block diagram in accordance with the present application;
fig. 3 is a control block diagram of a phase-locked loop-based network following type flexible dc converter according to the present application;
fig. 4 is an overall control block diagram of the flexible dc converter according to the present application;
fig. 5 is a control block diagram of a virtual synchronous machine of a soft dc converter according to the present application;
FIG. 6 is a block diagram of the current inner loop control in accordance with the present application;
fig. 7 is a schematic structural diagram of a network-structured flexible direct current system control based on a virtual synchronous machine.
Detailed Description
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. The present application may be embodied in many other forms than those herein described, and those skilled in the art will readily appreciate that the present application may be similarly embodied without departing from the spirit or essential characteristics thereof, and therefore the present application is not limited to the specific embodiments disclosed below.
Aiming at the defects of the prior art, the application provides a network-structured flexible direct current system control method based on a virtual synchronous machine, which has the flow shown in a figure 1, wherein a third-order virtual synchronous generator model based on a second-order rotor motion equation and a first-order transient voltage equation is applied to control a flexible direct current converter, so that a network-structured flexible direct current system control model is realized, and active support of power grid voltage, frequency and inertia is realized. The whole control block diagram of the net-structured flexible direct current method based on the improved virtual synchronous control is shown in fig. 4, and the internal control block diagram of the virtual synchronous machine is shown in fig. 5. The control strategy comprises the following steps:
step S101, a third-order virtual synchronous machine control model applied to the flexible direct current converter is established according to a second-order rotor model and a third-order generator model of the virtual synchronous machine.
An improved virtual synchronous control mathematical model. According to a second-order rotor model and a third-order generator model of the virtual synchronous machine, the influences of a virtual speed regulator, a rotor motion equation, a damping factor D, a rotor voltage balance equation and an excitation winding transient process are calculated, stator D and q winding transient processes are ignored, an improved virtual synchronous control model is simplified and obtained, specifically,
wherein θ is the internal potential virtual phase angle; omega is the virtual angular velocity of the controller; j is virtual inertia; p (P) m Is virtual mechanical power; p (P) e The active power is actually output for the flexible and straight system; d is a damping coefficient; omega 0 Is the angular velocity of the system; t (T) d ' 0 Is the excitation winding time constant; e's' q Is a transient potential; e (E) qe Is a forced no-load electromotive force; i.e d The d-axis current component is taken as the d-axis current reference value I of the converter output dref ；x d Is a synchronous reactance; x's' d Is the d-axis transient reactance.
Step S102, applying the third-order virtual synchronous machine control model, and responding to system frequency change by introducing a virtual speed regulator in the primary frequency modulation process of the virtual synchronous machine; and obtaining a synchronous generator rotor motion equation through sagging control.
Virtual speed regulation control link. And simulating a primary frequency modulation process of the synchronous generator set, introducing a virtual speed regulator, responding to the system frequency change, multiplying the frequency actual measurement value and the reference value by a droop coefficient after the deviation exceeds a dead zone link, generating additional power, and entering a rotor motion equation through droop control.
Wherein DeltaP ref Is an additional reference power; k (K) p Is a sagging coefficient; f (f) * Is the reference frequency; f is the measured frequency; f (f) deadzone To set the frequency dead zone.
Step S103, regarding the active power reference value of the converter as the mechanical power of the synchronous generator by simulating the motion equation of the rotor of the synchronous generator, and adjusting the rotating speed of the synchronous generator according to the change of the mechanical power so as to change the phase angle.
And a virtual rotor movement link. And simulating a synchronous generator rotor motion equation, regarding the active power reference value of the converter as the mechanical power of the synchronous generator, and adjusting the rotating speed according to the change of the mechanical power so as to change the phase angle. The rotor inertia integration link and damping component are introduced in the generation process of the phase angle, so that the power and the frequency approximate synchronize the generator in the dynamic process,
wherein DeltaP ref And (5) providing additional reference power for the virtual speed regulation control link.
During transients, the mechanical power of the synchronous generator may be considered approximately constant, while virtual synchronous control may improve the soft-dc converter transient characteristics by reducing the virtual mechanical power, reducing the risk of power angle instability.
Step S104, based on the third-order virtual synchronous machine control model, simulating a synchronous generator excitation voltage regulating system, taking the deviation of the net side alternating voltage measured value and the reference value as the input of the synchronous generator excitation voltage regulating system, and regulating reactive exchange of the soft direct current converter and the synchronous generator excitation voltage regulating system by changing the virtual internal potential amplitude.
Virtual excitation control link. Simulating an excitation voltage regulating system of the synchronous generator, taking the deviation of a net side alternating voltage measured value and a reference value as the input of the excitation voltage regulating system of the synchronous generator, changing the virtual internal potential amplitude value through PID amplitude limiting control, a lead-lag link, a rotor voltage balance equation and a first-order inertia link, further regulating reactive exchange of a soft direct current converter and the system,
wherein E is qe Is a forced no-load electromotive force in linear relation with the exciting voltage; k is the regulator gain; k (K) v Selecting a factor for proportional integral; t (T) 1 、T 2 、T 3 、T 4 Is the voltage regulator time constant; u (U) sref Is an inverter ac voltage reference value; u (U) s Is the actual measurement value of the alternating voltage; e (E) m The internal potential amplitude is output for the inverter.
Step S105, corresponding current reference values are calculated according to the phase angle, the virtual internal potential amplitude and the primary characteristics of the converter.
And a virtual circuit calculation link. And calculating a corresponding current reference value according to the virtual internal potential amplitude and the phase angle output by the improved virtual synchronous control and combining the primary characteristic of the converter. Assuming a prescribed internal potential dq axis reference value U cdref And U cqref The d-axis direction of (2) coincides with the virtual internal potential direction, and there are:
the current reference value is:
wherein I is dref +jI qref Is an output current reference value; u (U) cdref +jU cqref Is a virtual internal potential; u (U) sd +jU sq Is the actual ac side voltage; r+jx is the branch impedance.
Determining the limiting value I of the current according to the low-voltage current-limiting curve of the system-side alternating voltage dqlim And the current reference value after the limiting link enters the inner ring control again.
Step S106, taking the deviation of the current reference value and the real side value as input, and obtaining a voltage reference value of the soft direct current converter after superposition decoupling voltage and cross compensation; obtaining a voltage reference wave under the three-phase static coordinate-sensitive magic according to the phase angle of the virtual internal potential; and generating trigger pulses according to the voltage reference waves, and respectively controlling all sub-bridge arm sub-modules of the flexible direct current converter. The control block diagram is shown in fig. 6. And taking the deviation of the current reference value and the measured value as the input of the PI controller, superposing the decoupling voltage and the cross compensation term to obtain the voltage reference value of the flexible direct current converter, and then performing dq/abc conversion according to the phase angle of the virtual internal potential to obtain the voltage reference wave under the three-phase static coordinate system. And finally, generating trigger pulses according to the reference waves, and respectively controlling all bridge arm submodules of the flexible direct current converter.
Based on the same inventive concept, the application also provides a network-structured flexible direct current system control system based on a virtual synchronous machine, as shown in fig. 7, comprising:
the third-order model construction module 710 is configured to construct a third-order virtual synchronous machine control model applied to the flexible dc converter according to the second-order rotor model and the third-order generator model of the virtual synchronous machine;
the motion equation obtaining module is used for applying the third-order virtual synchronous machine control model, and responding to the system frequency change by introducing a virtual speed regulator in the primary frequency modulation process 720 of the virtual synchronous machine; obtaining a synchronous generator rotor motion equation through sagging control;
the phase angle obtaining module 730 is configured to, by simulating the equation of motion of the rotor of the synchronous generator, consider the active power reference value of the inverter as mechanical power of the synchronous generator, adjust the rotational speed of the synchronous generator according to the change of the mechanical power, and further change the phase angle;
the reactive power exchange module 740 is configured to simulate an excitation voltage regulating system of the synchronous generator based on the third-order virtual synchronous machine control model, take a deviation between a measured value of the network side ac voltage and a reference value as an input of the excitation voltage regulating system of the synchronous generator, and adjust reactive power exchange between the soft dc converter and the excitation voltage regulating system of the synchronous generator by changing a virtual internal potential amplitude;
a current reference value calculation module 750, configured to calculate a corresponding current reference value according to the phase angle, the virtual internal potential amplitude and the primary characteristics of the inverter;
the control module 760 is configured to take the deviation between the current reference value and the real side value as input, and superimpose the decoupling voltage and the cross compensation to obtain a voltage reference value of the soft dc converter; obtaining a voltage reference wave under the three-phase static coordinate-sensitive magic according to the phase angle of the virtual internal potential; and generating trigger pulses according to the voltage reference waves, and respectively controlling all sub-bridge arm sub-modules of the flexible direct current converter.
Further, the current reference value calculation module includes:
a calculation sub-module for assuming a prescribed internal potential dq axis reference value U cdref And U cqref The d-axis direction of (2) coincides with the virtual internal potential direction, and there are:
the current reference value is:
wherein I is dref +jI qref Is an output current reference value; u (U) cdref +jU cqref Is a virtual internal potential; u (U) sd +jU sq Is the actual ac side voltage; r+jx is the branch impedance.
Further, the method further comprises the following steps:
a limiting submodule for determining the limiting value I of the current according to the low-voltage current-limiting curve of the system side alternating voltage dqlim And the current reference value after the limiting link enters the inner ring control again.
According to the control method and system for the net-structured flexible direct current system based on the virtual synchronous machine, the third-order generator model is referenced on the basis of the virtual synchronous control second-order model, and the transient processes of the speed regulator and the exciting winding are considered, so that the flexible direct current system has the capabilities of improving the voltage and frequency stability of the system and enhancing the inertia and damping of the system. The control method can flexibly perform island/networking operation mode conversion, can effectively solve the problem that a flexible direct-current control strategy is not suitable for caused by the change of the power grid strength, and is an important foundation for popularization and application of the network construction type flexible direct-current transmission technology.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present application and not for limiting the same, and although the present application has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that modifications and equivalents may be made to the specific embodiments of the present application without departing from the spirit and scope of the present application, and it should be covered by the scope of the claims of the present application.
Claims (10)
1. A control method of a network-structured flexible direct current system based on a virtual synchronous machine is characterized by comprising the following steps:
establishing a third-order virtual synchronous machine control model applied to the flexible direct current converter according to a second-order rotor model and a third-order generator model of the virtual synchronous machine;
applying the third-order virtual synchronous machine control model, and responding to the system frequency change by introducing a virtual speed regulator in the primary frequency modulation process of the virtual synchronous machine; obtaining a synchronous generator rotor motion equation through sagging control;
the method comprises the steps of simulating a rotor motion equation of the synchronous generator, regarding an active power reference value of an inverter as mechanical power of the synchronous generator, and adjusting the rotating speed of the synchronous generator according to the change of the mechanical power so as to change a phase angle;
based on the third-order virtual synchronous machine control model, simulating an excitation voltage regulating system of the synchronous generator, taking the deviation of a net side alternating voltage measured value and a reference value as the input of the excitation voltage regulating system of the synchronous generator, and regulating reactive exchange of the soft direct current converter and the excitation voltage regulating system of the synchronous generator by changing the virtual internal potential amplitude;
calculating a corresponding current reference value according to the phase angle, the virtual internal potential amplitude and the primary characteristic of the converter;
taking the deviation of the current reference value and the real side value as input, and obtaining a voltage reference value of the soft direct current converter after superposition decoupling voltage and cross compensation; obtaining a voltage reference wave under the three-phase static coordinate-sensitive magic according to the phase angle of the virtual internal potential; and generating trigger pulses according to the voltage reference waves, and respectively controlling all sub-bridge arm sub-modules of the flexible direct current converter.
2. The method of claim 1, wherein establishing a third-order virtual synchronous machine control model for the flexible dc converter based on the second-order rotor model and the third-order generator model of the virtual synchronous machine comprises:
according to a second-order rotor model and a third-order generator model of the virtual synchronous machine, the influences of a virtual speed regulator, a rotor motion equation, a damping factor D, a rotor voltage balance equation and an excitation winding transient process are calculated, stator D and q winding transient processes are ignored, an improved virtual synchronous control model is simplified and obtained, specifically,
wherein θ is the internal potential virtual phase angle; omega is the virtual angular velocity of the controller; j is virtual inertia; p (P) m Is virtual mechanical power; p (P) e The active power is actually output for the flexible and straight system; d is a damping coefficient; omega 0 Is the angular velocity of the system; t (T) d ' 0 Is the excitation winding time constant; e's' q Is a transient potential; e (E) qe Is a forced no-load electromotive force; i.e d The d-axis current component is taken as the d-axis current reference value I of the converter output dref ；x d Is a synchronous reactance; x's' d Is the d-axis transient reactance.
3. The method of claim 1, wherein obtaining the synchronous generator rotor equation of motion by droop control comprises:
when the deviation between the measured value and the reference value of the system frequency exceeds the dead zone link, multiplying the dead zone link by a droop coefficient to generate additional power, performing a rotor motion equation through droop control,
wherein DeltaP ref Is an additional reference power; k (K) p Is a sagging coefficient; f (f) * Is the reference frequency; f is the measured frequency; f (f) deadzone To set the frequency dead zone.
4. The method of claim 1, wherein adjusting the rotational speed of the synchronous generator to change the phase angle based on the mechanical power change comprises:
the rotor inertia integration link and damping component are introduced in the generation process of the phase angle, so that the power and the frequency approximate synchronize the generator in the dynamic process,
wherein DeltaP ref And (5) providing additional reference power for the virtual speed regulation control link.
5. The method of claim 1, wherein the step of using the deviation of the net side ac voltage measurement value from the reference value as an input to the synchronous generator excitation voltage regulation system to regulate reactive exchange of the flexible dc converter with the synchronous generator excitation voltage regulation system by varying the virtual internal potential magnitude comprises:
the deviation of the net side alternating voltage measured value and the reference value is used as the input of the excitation voltage regulating system of the synchronous generator, the virtual internal potential amplitude is changed through PID amplitude limiting control, a lead-lag link, a rotor voltage balance equation and a first-order inertia link, and then the reactive power exchange between the soft direct current converter and the system is regulated,
wherein E is qe Is a forced no-load electromotive force in linear relation with the exciting voltage; k is the regulator gain; k (K) v Selecting a factor for proportional integral; t (T) 1 、T 2 、T 3 、T 4 Is the voltage regulator time constant; u (U) sref Is an inverter ac voltage reference value; u (U) s Is the actual measurement value of the alternating voltage; e (E) m The internal potential amplitude is output for the inverter.
6. The method of claim 1, wherein calculating a corresponding current reference value from the phase angle, virtual internal potential magnitude, and inverter primary characteristic comprises:
assuming a prescribed internal potential dq axis reference value U cdref And U cqref The d-axis direction of (2) coincides with the virtual internal potential direction, and there are:
the current reference value is:
wherein I is dref +jI qref Is an output current reference value; u (U) cdref +jU cqref Is a virtual internal potential; u (U) sd +jU sq Is the actual ac side voltage; r+jx is the branch impedance.
7. The method as recited in claim 6, further comprising:
determining the limiting value I of the current according to the low-voltage current-limiting curve of the system-side alternating voltage dqlim And the current reference value after the limiting link enters the inner ring control again.
8. A network-structured flexible direct current system control system based on a virtual synchronous machine is characterized by comprising:
the third-order model construction module is used for building a third-order virtual synchronous machine control model applied to the flexible direct current converter according to the second-order rotor model and the third-order generator model of the virtual synchronous machine;
the motion equation obtaining module is used for applying the third-order virtual synchronous machine control model, and responding to the system frequency change by introducing a virtual speed regulator in the primary frequency modulation process of the virtual synchronous machine; obtaining a synchronous generator rotor motion equation through sagging control;
the phase angle obtaining module is used for regarding the active power reference value of the converter as the mechanical power of the synchronous generator by simulating the motion equation of the rotor of the synchronous generator, and adjusting the rotating speed of the synchronous generator according to the change of the mechanical power so as to change the phase angle;
the reactive power exchange module is used for simulating an excitation voltage regulating system of the synchronous generator based on the third-order virtual synchronous machine control model, taking the deviation of the net side alternating voltage measured value and the reference value as the input of the excitation voltage regulating system of the synchronous generator, and adjusting the reactive power exchange of the soft direct current converter and the excitation voltage regulating system of the synchronous generator by changing the virtual internal potential amplitude;
the current reference value calculation module is used for calculating a corresponding current reference value according to the phase angle, the virtual internal potential amplitude and the primary characteristic of the converter;
the control module is used for taking the deviation of the current reference value and the real side value as input, and obtaining the voltage reference value of the soft direct current converter after superposition decoupling voltage and cross compensation; obtaining a voltage reference wave under the three-phase static coordinate-sensitive magic according to the phase angle of the virtual internal potential; and generating trigger pulses according to the voltage reference waves, and respectively controlling all sub-bridge arm sub-modules of the flexible direct current converter.
9. The system of claim 8, wherein the current reference calculation module comprises:
a calculation sub-module for assuming a prescribed internal potential dq axis reference value U cdref And U cqref The d-axis direction of (2) coincides with the virtual internal potential direction, and there are:
the current reference value is:
wherein I is dref +jI qref Is an output current reference value; u (U) cdref +jU cqref Is a virtual internal potential; u (U) sd +jU sq Is the actual ac side voltage; r+jx is the branch impedance.
10. The system of claim 9, further comprising:
clipping sub-dieA block for determining the limiting value I of the current according to the low-voltage current-limiting curve of the system side alternating voltage dqlim And the current reference value after the limiting link enters the inner ring control again.
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| CN117871929A (en) * | 2024-02-05 | 2024-04-12 | 中国电力科学研究院有限公司 | Method and device for determining maximum current of SVG during transient overvoltage suppression |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117353338A (en) * | 2023-12-06 | 2024-01-05 | 广东电网有限责任公司珠海供电局 | M3C-based active support control system and device for virtual synchronous machine |
| CN117353338B (en) * | 2023-12-06 | 2024-04-02 | 广东电网有限责任公司珠海供电局 | M3C-based active support control system and device for virtual synchronous machine |
| CN117871929A (en) * | 2024-02-05 | 2024-04-12 | 中国电力科学研究院有限公司 | Method and device for determining maximum current of SVG during transient overvoltage suppression |
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